1. Field of the Invention
The invention generally relates to control signaling over access channels in mobile communication systems, and more particularly, to access procedure enhancements for mobile communication systems.
2. Description of the Related Art
For a long time, various machines have been provided to make our lives more convenient in every way. Generally, machines, nowadays, are equipped with computing processors and software to accommodate us with more intelligence-based services. With the advancement of wireless communications, Machine-to-Machine (M2M) technology has been developed to enable communications between remote machines for exchanging information and operating without human interaction. Especially for critical public infrastructures, such as water treatment facilities or bridges, M2M sensors may be employed to monitor the operation statuses of facilities and report measurement results back to control centers via wireless communication networks, such as Global System for Mobile Communication/General Packet Radio Service (GSM/GPRS), Universal Mobile Telecommunication System (UMTS), 1x Code Division Multiple Access 2000 (1x CDMA 2000) system, 1x High Rate Packet Data (1xHRPD) system, and Long Term Evolution (LTE) system, etc. This would allow administrators of the critical public infrastructures to know if certain elements have been tampered with. Other applications may be electric meters, gas line monitoring devices, or coke machines that report their operation statuses to a centralized system via wireless communication networks, to provide related services with higher efficiency and lower maintenance costs.
It is noted that the amount of data per report is usually small, so preferably, an access channel is used by most M2M machines to transmit the data traffic. FIG. 1 is a block diagram illustrating a conventional access procedure of an M2M machine. To begin, the M2M machine first performs a persistence check to see if another M2M machine is transmitting data on the access channel. If not, it transmits an access probe with an initial transmission power. Subsequently, the M2M machine waits for a response of the access probe for a period of time (denoted as Tp). If no response of the access probe is received during Tp, the M2M machine increases the transmission power and uses the increased transmission power to retransmit the access probe. During each probe sequence, the retransmission of the access probe is repeated using incremental transmission power until a response of the access probe is received or a maximum number of retries (denoted as Np) is reached. If no response of the access probe is received during a probe sequence of retransmission, the M2M machine further holds for another period of time (denoted as Ts) and then initiates another probe sequence of retransmission. However, it is noted that the access channel is a shared common channel for all M2M machines in the same service area and too many retransmissions of the access probe may cause unnecessary occupancy over the access channel. That is, collision of access probes transmitted by different M2M machines may occur frequently and result in throughput degression for the entire M2M system.
In addition, when selecting an access network (referred to as AN herein) to initiate the access procedure, the conventional M2M machine only takes into account the pilot strength of the detected ANs, and transmits the access probe to the AN with the highest pilot strength. However, if the reverse-link (referred to as RL herein) load of the selected AN is heavy, the interference on the RL will be great. In this case, the delivery of the access probe is not only likely to fail, but also introduces more interference on the RL. Thus, it is desirable to have a novel access procedure in which the radio resources of the access channel may be efficiently utilized to improve the overall system throughput.